I'd search Apple's Knowledge Database... Also: What Mac do you have specifically? Was the firmware update intended for your machine? Has Apple already released a newer version for your specific machine? My guess is you have an 1.6 GHz PowerMac G5 and installed the update for 'single-processor' PowerMacs that was only intended for 1.8 GHz machines (but badly labelled...). If so, I thought Apple had already released an updated firmware for your machine.